Introduction: tween 80 is one of the important excipients that have been widely used in food and drugs industries. Although this compound considered to be safe for human use, there have been reports of liver toxicity in patients taking drug formulations containing this substance. Thus, the objective of the present research was to evaluate the sub-acute toxicity of tween 80 in male Wistar rats. Materials and methods: twenty-four male Wistar rats weighing 200-240 g at the beginning of the experiments were used in this research. The rats were purchased from Pasture institute (Tehran-Iran) and after transport to the animal house of University of Maragheh spent a seven days adaptation period. Standard maintenance conditions were provided for the animals before and during the experiments. For the sub-acute toxicity study, four groups of animals received once daily injection of saline and different concentration of tween 80 (1%, 5%, and 10%, ml/kg) in normal saline, intraperitoneally for two weeks. On day 15, the animals were anesthetized by Ketamine (80 mg/kg, i.p.) and xylazine (20 mg/kg, i.p.) and blood and serum samples were harvested for analyzing urea, creatinine, AST, ALT, and ALP, and blood parameters. Results: no death was occurred in the animal groups that received tween80. The weight of rats that received the high dose of tween 80 showed a significant decrease compared to that of the saline-treated group. In terms of blood parameters, compared to saline-treated animals, the rats that received tween 80 (in high dose) showed a decrease in HGB, HCT, MCV, and MCH that indicates anemia. Moreover, a significant increase in ALT, AST, and ALP was shown in the tween 80-treated rats. At last, analysis of serum samples showed that administration of tween80 increased blood urea nitrogen but had no effect on creatinine. Conclusion: The present study showed that tween 80 (especially in high concentrations) may have some toxic effects on the blood, liver, and kidney, and so th
